Like many countries, Brazil has a deregulated electricity market and all the players are bound by the rules set by ANEEL, the Brazilian regulatory agency. This agency has introduced harsh penalties for both scheduled and unscheduled outages. For example, the financial penalty imposed for an unscheduled fault outage can be 150 times the expected revenue or revenue lost for the first five hours of this outage. Naturally, this regulatory standard is the impetus for all utilities to focus their efforts on improving system security by preventing outages and improving the maintenance of their equipment.

The Brazilian utility Furnas Centrais Elétricas SA (Furnas; Rio de Janeiro, Brazil), like most utilities, employed a preventive-maintenance program, whereby it maintained equipment on a scheduled basis, according to the manufacturer's recommendations and the experience of its engineers. The maintenance of equipment was not based on the actual condition of equipment or a policy of condition-based maintenance (CBM).

Furnas, therefore, had to take measures to meet the new rules imposed by ANEEL. The utility examined real-time monitoring of its equipment as a means of reducing both scheduled and unscheduled system outages. As a result, Furnas introduced an intranet-controlled on-line monitoring system to provide information on the state of equipment within its substations.

Furnas' Operational Network

Furnas operates in the southern half of Brazil, an area that includes the capital, Brazilia, and the major cities of Rio de Janeiro and São Paulo. The utility supplies electrical energy to almost half of the population of Brazil via 12 power-generation stations, 43 substations and a 18,000-km (11,200-mile) transmission system, which used a preventive-maintenance philosophy prior to ANEEL's regulatory changes.

Furnas began development studies for a real-time monitoring system in 1999. Initially, the utility planned to install a system that only applied to transformers. Following discussions with several transformer manufacturers in the meeting with ALSTOM, Furnas was introduced to the manufacturer's MS2000 transformer on-line monitoring system. Because this system satisfied all the utility's requirements and several MS2000 units were in service, Furnas engineers went to Germany to see the first system that was installed in 1995.

Following this pre-evaluation of all the available monitoring systems, Furnas prepared a technical specification and awarded ALSTOM a contract to supply the utility's first system. The MS2000 transformer on-line monitoring system not only complied with the Furnas' specifications, but it also offered the opportunity to extend the system monitoring at a later date to include all key electrical equipment in the substation

Real-Time Monitoring System

A monitoring system collects information from several measurable variables, which are defined by the age and condition of the transformer. Depending on the transformer's operational duty, the range of variable transformer parameters that can be measured includes: top oil temperature, ambient temperature, load current, operational voltage, overvoltages at the bushings, bushing oil pressure, moisture content of the oil, gas-in-oil content, switching status of fans and pumps, tap changer position, and the power consumption of the motor that drives the load tap changer.

These variables are all considered to be important as they are linked to the most frequent and common causes of transformer failure. Additional information such as hot-spot temperature, aging rate, lifetime consumption, overload capacity or change of the bushing capacitance can be evaluated from the sensors. The system also provides a diagnosis and prognosis of incipient failures for maintenance programming.

The outputs from these sensors are collected in the monitoring module installed on the transformer. The signals are then digitized and sent via a field bus to the monitoring server. The system monitors all the transformers installed in a substation via a single server. Fiber-optic and field bus technologies are two examples of the communications systems that can be used to reduce the wiring and installation costs associated with conventional technology. While researching transformer-monitoring systems, Furnas purchased and installed monitoring systems on the most important transformers located in strategically positioned transmission substations. It then prepared on-line monitoring system specifications for breakers and switches.

Substation Monitoring System

In accordance with the utility's objective to change the maintenance philosophy from a preventive to a predictive discipline throughout the complete network, Furnas invited ALSTOM to integrate the CBWatch-2 circuit-breaker monitoring system into the MS2000 system by means of a serial field bus. The CBWatch-2, developed by ALSTOM in France, is also integrated into the overall system, therefore, the output data can be viewed via the MS2000 on the Furnas intranet.

CBWatch-2 monitors SF6 circuit breakers using a micro-controller installed in the drive of the circuit breaker. This monitoring unit has options for monitoring gas density, leakage rate and the mechanical operation of the circuit breaker via travel curve analysis for supervision of spring loading operating time. The monitoring also measures the interrupted current, primary contact wear and arcing time for surveillance of the auxiliary and trip circuits. Furthermore, the performance of disconnector switches, based on the measured power consumption of the motor drive during switching, can be connected to the overall MS2000 system.

The utility specified that it has intranet access to the data, provided the data can be accessed from any PC using standard software, such as Microsoft's Internet Explorer. By requiring intranet access, Furnas avoided installing special software on individual computers and gained better flexibility in terms of granting or removing access to its employees. ALSTOM made the necessary adaptations to the MS2000 system, and in January 2001, Furnas awarded ALSTOM a contract to install the system at the Samambaia Substation. The system was installed and commissioned in the following year.

Since then, Furnas has awarded ALSTOM additional contracts in two stages for installations at four substations: Agua Vermelha, Mascarenhas de Moraes, Ibiúna and Bateias.

At its headquarters in Rio, the utility is installing the server that will oversee the monitoring system, and engineers will be able to access the date via the utility's intranet. Each substation will be fitted with a firewall that allows access to only certain TCP/IP addresses. Passwords for both employees and equipment will allow Furnas to protect access and data, but the flexibility of the system will allow authorized staff to access the system from wherever they are working.

Advantages and Cost Benefits

The advantage of a monitoring system is its inherit ability to give an accurate picture of the operating condition of the transformer, allowing the operator to detect the early signs of faults and correct them. It also provides the tools, in the form of data, to plan maintenance on the basis of the actual condition of the transformer and avoid unnecessary maintenance work. The information gives operators the ability to estimate with great accuracy the remaining lifetime of a transformer and defer investment in new equipment.

Cost savings achieved by avoiding system transformer failures and downtimes are critical for Furnas. Based on the available failure statistics of large power transformers and the experience of more than 120 installations of MS2000 systems, ALSTOM estimates the reduced cost of major failure to yield an average saving equivalent to 5% of the capital cost of a transformer over 10 years. This calculation does not take into account the cost of repairing any collateral damage caused by a transformer failure to other equipment in the substation. Preventing unplanned outages caused by transformer failure is the most important financial benefit, as it helps to guarantee Furnas' contractual obligations with ANEEL.

Furnas' strategy of implementing such technology is a significant milestone in the development of new maintenance techniques that it believes will signal a change in maintenance policy with other utilities. In the long term, the utility plans to increase the benefits further by continuing the installation of this real-time monitoring system in the utility's most important and strategic transmission substations.

Gilson Bastos received his degree from Rio de Janeiro Catholic University in 1979 and joined Furnas in Rio de Janeiro, where he is now head of the electrical equipment division. He is a member of Brazil's CIGRÉ Committee A2-Power Transformers and the Brazilian Transformers Standard Committee CE 14 Power Transformers.

gbastos@furnas.gov.br